Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

New snow and strong winds overnight will form wind slabs in exposed terrain.  These wind slabs and new snow will be deposited on top of a weak snowpack and may not bond well to the previous snow surface.  Dangerous avalanche conditions exist with multiple avalanche problems present.  Cautious route finding and decision making is critical if traveling in the backcountry today.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Up to a foot of new snow with strong to gale force winds overnight have created wind slabs in near and above treeline areas.   These wind slabs will form on the downwind side of ridgetops where drifting snow is deposited.  Wind slabs could also form on top of recently buried surface hoar or near surface facets that existed on the snow surface before this storm.  These wind slabs would be much easier to trigger and could break wider than expected.  The possibility also exists that areas with large wind drifts could overload our weak faceted snow near the ground, causing much larger and destructive avalanches to occur.  

    Look for areas where blowing snow is actively occurring, where cornices or wind drifts have formed, and for any areas of snow surface cracking.  Snow surface scouring may also help to determine where previous blowing snow was occurring as wind direction changes today.  Use these clues to identify areas of potentially unstable wind slab and move around these areas with caution.

    (12/28/2023)

    An avalanche that occurred on Dec 20, likely naturally triggered during an intense period of new snowfall and wind loading. This was an instance of deeper persistent weak layer failure in a wind loaded area.

    Photo: Public

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    A weak snowpack structure continues throughout the forecast region with weak faceted snow near the base of our snowpack in most locations above around 8500' in elevation.  This current storm is not likely enough additional load to cause failure on this weak layer.  In areas where this weak layer exists that received additional wind blown snow, avalanches could be possible.  Any avalanches on this weak layer near the ground would be large and destructive with severe consequences.

    In additional to the well-defined faceted weak layer near the base of our snowpack-there is potential for multiple weak layers on the old snow surface to be buried by this current storm.  Well-developed surface hoar has been reported in multiple areas yesterday and could be buried under this current storm.  Also, areas of near surface facets exist on the snow surface on NW-N-NE aspects at most all elevations.  Areas with wind blown snow or places that received the higher end storm totals will be the most likely to have avalanches occur on these weak layers.

    Recent avalanche activity, cracking in the snow, or whumpfing sounds, will be signs that unstable snow exists.  If traveling in the backcountry today, move through terrain cautiously with wide safety margins away from avalanche terrain. 

    (1/2/2024)

    Large surface hoar in the Carson Pass area.

    Photo: SAC

Avalanche Discussion

The snowpack is usable, mainly on NW-N-NE-E aspects above 7,500 to 8,300 ft depending on location. Periods of melt have caused the lower limit of the usable snowpack to creep upwards in elevation. Expect obstacles: rocks, bushes, trees stumps, and open water to encounter when traveling in the backcountry.

Regions covered